This invention relates to a drive arrangement for a rotating unit, such as a rotary drum, drum mill or the like, comprising a main motor, a main transmission unit arranged between the main motor and the unit to be driven, an auxiliary motor, an auxiliary transmission unit arranged between the auxiliary motor and the main transmission unit, a centrifugal brake arranged between the auxiliary motor and the main motor, and an overriding clutch for overriding the auxiliary transmission unit.
In addition to a main motor and a main transmission unit, drive arrangements of the type used in particular for relatively large rotating units, such as rotary kilns, drum mills and the like, comprise an auxiliary transmission unit which is driven by an auxiliary motor and of which the output shaft is also drivingly connected to an input shaft of the main transmission unit. The auxiliary transmission unit may be used for example to drive the rotating unit up to a certain rotational speed via the main transmission unit during the start-up phase, after which the main motor for the main drive is engaged with its higher rotational speed for full-load operation. An overriding clutch is used in the transmission link between the auxiliary transmission unit and the main transmission unit, establishing a flexible connection between the auxiliary transmission unit and the main transmission unit in one direction of rotation. After a certain rotational speed has been reached and after the main motor has been engaged, this flexible connection is broken by "overriding;" in other words the drive from the auxiliary transmission unit to the main transmission unit and to the rotating unit is suspended. In addition, the auxiliary transmission unit with the auxiliary motor is important in assembly or repair work when the rotating unit has to be rotated slowly and at intervals.
If for example a rotary kiln or a drum mill is driven by an auxiliary motor in conjunction with an auxiliary transmission unit, it occasionally happens that this unit seeks to lead the drive which, in the case of a rotary kiln equipped with planetary cooling tubes, can occur for example when one of the cooling tubes has been removed or otherwise even when deposits or the like have built up within the unit on one side thereof. This leading of the drive or even merely leading final oscillations of the rotating unit can endanger the drive elements on account of the increased rotational speed involved.
Various types of drive arrangements have become known in practice for counteracting the above-mentioned problems. For example, attempts have been made to arrange a shiftable gear coupling between the main transmission unit an the auxiliary transmission unit in a drive arrangement for a rotary kiln. Although a gear coupling such as this is basically suitable for transmitting varying torques, it is only possible in this case to obtain final oscillation of the rotary kiln (for example after the drive has been switched off) by an electrically braked main motor or by an additionally installed differential recoil brake which enables the gear coupling to be introduced. However, constructions such as these have never been adopted for use in practice on account of the labile braking behavior.
Since, in cases where overriding clutches are used, they are unable to prevent the rotating unit from automatically leading, the search for effective solutions has continued.
Another embodiment which is known in practice contains between the main motor and main transmission unit double-shoe brakes which, although capable of stopping a rotary kiln for example from leading while it is stationary, are attended by the disadvantage that unintentional braking during operation can have a damaging effect on driving components. Although the differential recoil brakes mentioned above--should it be desired to use them instead of the double-shoe brakes--do not have a damaging effect in the event of unintentional braking during operation, they do have the disadvantage that, in this event, they are also unable to prevent the rotating unit from leading.